The present invention relates to a solid-state image pickup device and a driving method of a solid-state image pickup device, and particularly to a solid-state image pickup device and a driving method of a solid-state image pickup device that perform readout by making a potential of a vertical charge transfer region (hereinafter referred to as a vertical CCD) sufficiently deep and extending a depletion layer of the vertical CCD in a direction of a sensor by a voltage applied to a vertical transfer electrode.
In a unit pixel structure of an interline (IT type) CCD solid-state image pickup device, which is the current mainstream of CCD solid-state image pickup devices, and a frame interline (FIT type) CCD solid-state image pickup device used for broadcasting stations and the like, basically as shown in a schematic structural sectional view of FIG. 1 and a plan layout view of FIG. 2 (a scale of FIG. 2 does not correspond with a scale of FIG. 1), a sensor region 121 for performing photoelectric conversion and charge accumulation is formed in a P-type well 112 formed in a semiconductor substrate 110. Formed on one side of the sensor region 121 are a readout gate region 122 for transferring a charge to a vertical CCD and the vertical CCD 123 for transferring the charge read out by the readout gate region 122, with the readout gate region 122 intermediate between the sensor region 121 and the vertical CCD 123. Further, a channel stop region 125 is formed between the pixel 111 and a pixel (not shown) adjacent to the pixel 111. Further, a transfer electrode 127 is formed on the vertical CCD 123 (including a channel region 124), the readout gate region 122, and the channel stop region 125 with an insulating film 126 interposed between the transfer electrode 127, and the vertical CCD 123, the readout gate region 122, and the channel stop region 125. Further, an opening 130 is formed on the sensor region 121, and a light shielding electrode 129 for covering the transfer electrode 127 is formed with an interlayer insulating film 128 interposed between the transfer electrode 127 and the light shielding electrode 129 (see Patent Literature 1, for example).
In a case of construction of a CCD having a pixel 2.5 μm square, for example, supposing that the channel stop region 125 has a width of 0.35 μm, the readout gate region 122 has a width of 0.35 μm, and the sensor region 121 has a width of 1.0 μm, the channel region 124 of the vertical CCD 123 has a width of 0.8 μm. With the conventional structure, it is becoming difficult to maintain characteristics regarding sensitivity, an amount of charge handled by the sensor region 121, smears, an amount of charge handled by the vertical CCD 123, and the like as CCD unit cells are scaled down.
In order to solve these problems, a solid-state image pickup device of a punch-through readout structure has been disclosed (see Non-Patent Literature 1 and Patent Literature 2, for example).
[Patent Literature 1]
    Japanese Patent Laid-Open No. Hei 6-151792 (pp. 2-3, FIG. 1)[Patent Literature 2]    Japanese Patent Laid-Open No. Hei 10-70263 (pp. 3-4, FIG. 1)[Non-Patent Literature 1]
Toshifumi Ozaki, H. Ono, H. Tanaka, A. Sato, M. Nakai, and T. Nishida, IEEE TRANSACTION ON ELECTRON DEVICES, VOL. 41, NO. 7, (1994), PP. 1128-1134
In order to increase the amount of charge handled by the vertical CCD without increasing the area, there is a method of increasing the capacitance by forming a thinner gate insulating film or densely forming a channel dopant. However, these methods have a disadvantage of making charge transfer difficult. While increase in driving amplitude of the vertical CCD results in increase of the amount of charge handled, VHigh voltage is set as negative voltage in a present situation because plus side driving of VHigh in the conventional structure increases dark current.